This invention relates to bolt-on, duplex circuit breakers, and more particularly to an assembly which includes the bolt-on circuit breaker and the panelboard into which it is inserted.
For many years, plug-in, duplex circuit breakers have been manufactured for use within electrical panelboards. These plug-in breakers have typically been manufactured to fulfill the Underwriter Laboratories Inc. standard UL67, "Standard for Panelboards", Guide No. 320 BO File E31679 and E52977, so as to entitle these breakers to UL approval. UL67 states that these breakers and the panelboard into which they are fitted must be manufactured so as to permit installation of no more breaker units than that for which the panelboard was intended. UL67 further states that installation of more breaker units than intended within the panelboard is considered capable of being accomplished if it is possible to force a breaker unit, without deliberate modification of either the unit or the panelboard, into position in a space not intended to receive it or if it is possible to modify the breaker unit using specifically described tools (i.e. electrician's tools) to permit mounting the unit within the panelboard. To fall within these guidelines, plug-in breakers have been manufactured with a well known rejection feature.
The rejection feature employed by plug-in, duplex circuit breakers is designed around the plug-in construction of the device. The line terminal of plug-in breakers is manufactured with internal spring clips while the panelboard line bus is manufactured with stabs. When a breaker is mounted within the panelboard, the line side spring clip engages the line bus stab thereby securing the breaker within the panelboard and completing the electrical connection. To fulfill the requirements of UL67, the plug-in breaker is manufactured with a rejection tab positioned within the insulating casing of the breaker extending along the line terminal spring clips while the line bus stabs are manufactured with a correspondingly notched vertical groove. This tab-notch combination allows the breaker to be plugged only onto those stabs that are manufactured specifically to accept the breaker. The location of the rejection tab internally within the breaker further fulfills the unmodifiable requirement of UL67.
The need for a better means of securing a breaker within a panelboard and for better electrical connections gave rise to the invention of the bolt-on, duplex circuit breaker. The bolt-on breaker is manufactured by replacing the internal line terminal spring clips with an external mounting flange having a centrally disposed opening, while the line bus stabs are replaced with bolting assemblies to which the breaker flange is bolted. While this accomplishes the desired results, the rejection feature employed by the plug-in breakers can not be utilized with this design. As a result, bolt-on breakers have the problem of not being able to meet the safety requirements imposed by UL67.